When boreholes are drilled to recover oil or gas the well casing dropped into the hole is usually cemented to the formation at or near the lower end of the hole, and at other locations along the casing. In cementing the casing to the formation the formation is sealed to the casing in the annulus outside of the casing. Production from the oil well or gas well is through perforations in the casing and cement, into the casing and then upward to the wellhead.
In the production of heavy viscous crudes which require some form of modification to the crude itself in the subsurface in order to make it producible into a casing, it has become necessary to seal the inside of the cased well so as to establish a zone within the cased well through which materials may be pumped from the casing into the formation. In the typical operation, an expandable packer is placed on the end of a packer-placing or injection tubing and the packer is expanded to completely seal the annulus between the casing and the placing or injection tubing.
When steam or hot liquids are the material that is being pumped into the formation, the expandable packer is less desirable and ineffective because expandable materials are incapable of sustaining the desired seal when the injection temperatures are 300.degree. F. and higher and the injection pressures can be of the order of 2000 to 2500 pounds per square inch. Alternative means for sealing the annulus along the cased well are, therefore, needed in the event that the fluids pumped into the well are at high temperatures and pressures.